An implementation of the Boyer-Moore string search algorithm in Clojure. The Wikipedia entry for this algorithm describes it thusly:
The Boyer-Moore algorithm searches for occurrences of P in T by performing explicit character comparisons at different alignments. Instead of a brute-force search of all alignments (of which there are m-n+1), Boyer-Moore uses information gained by preprocessing P to skip as many alignments as possible.
Previous to the introduction of this algorithm, the usual way to search within text was to examine each character of the text for the first character of the pattern. Once that was found the subsequent characters of the text would be compared to the characters of the pattern. If no match occurred then the text would again be checked character by character in an effort to find a match. Thus almost every character in the text needs to be examined.
The key insight in this algorithm is that if the end of the pattern is compared to the text, then jumps along the text can be made rather than checking every character of the text. The reason that this works is that in lining up the pattern against the text, the last character of the pattern is compared to the character in the text. If the characters do not match there is no need to continue searching backwards along the pattern. If the character in the text does not match any of the characters in the pattern, then the next character to check in the text is located n characters farther along the text, where n is the length of the pattern. If the character is in the pattern then a partial shift of the pattern along the text is done to line up along the matching character and the process is repeated. The movement along the text in jumps to make comparisons rather than checking every character in the text decreases the number of comparisons that have to be made, which is the key to the efficiency of the algorithm.
This clojure implementation is designed to work on strings, sequences, vectors,
and java.io.InputStream. Ported from the original:
https://github.com/rm-hull/cljs-dataview/blob/master/src/dataview/boyer_moore.cljs.
You will need Leiningen 2.8.1 or above installed.
To build and install the library locally, run:
$ cd boyer-moore-search
$ lein test
$ lein install
There is a version hosted at Clojars. For leiningen include a dependency:
[rm-hull/boyer-moore-search "0.1.0"]For maven-based projects, add the following to your pom.xml:
<dependency>
<groupId>rm-hull</groupId>
<artifactId>boyer-moore-search</artifactId>
<version>0.1.0</version>
</dependency>TODO
Copyright (c) 2016 Richard Hull
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